1. Field of the Invention
This invention relates to a fault interruption device that is configured for wall receptacle applications. By utilizing a special switch configuration, the fault interruption device may be installed with swapped line and load terminals with no loss of protection to local and remote outlets. Ground assurance, open neutral detection and line reversal detection are easily incorporated along with a self testing capacity, enabling a versatile, low cost fault interrupter that presents a high degree of protection against wiring conditions that may compromise safety.
2. Background of the Invention
Ground fault current interrupters (GFCIs) are devices that are often used in load centers and in receptacle outlets in commercial and residential buildings. These devices protect against undesirable electrical leakages to earth ground by sensing current imbalances in the power delivery conductors and interrupting power delivery upon the occurrence of a possibly hazardous leakage condition. Another type of device, called an arc fault current interrupter (AFCI), is used to detect high energy discharges between electrified objects in a distribution network or from one electrified object to ground. Both GFCIs and AFCIs are required by code to be installed in particular locations in dwellings and commercial construction and both devices are occasionally co-located. Although AFCIs and GFCIs protect against different types of events, they have a similar construction and encounter similar problems and the present patent will refer to both types of devices as fault interrupters.
A malfunctioning fault interrupter will not provide protection. Malfunctions may occur due to two broad categories of source: defect or incorrect installation. First, a malfunction may occur due to a defect in design or performance of the fault interrupter or to the malfunction of one or more constituent components. Second, a malfunction may occur if the fault interrupter is incorrectly installed or if required electrical connections to the fault interrupter become loose or are damaged.
In the U.S., electrical distribution networks generally provide power to the home or office via a grounded neutral system. That is, of the two power delivery conductors, one is typically electrically connected to ground at one or more points within the system. This grounded power delivery conductor is known as “neutral”. The other, ungrounded conductor, is generally referred to as “hot”.
Many fault interrupters are configured as wall receptacle units. These receptacle interrupters generally have one or more local outlets built into the unit and into which an electrical appliance may be plugged. These receptacle fault interrupters often have two sets of electrical connection points called line and load. The line side electrical connection points are designated for connection to the power source. The load side electrical connection points are designated for connection to additional electrical branches which, in turn, may serve as the source for remote electrical outlets. When the fault interrupter is correctly installed, fault protection is provided to both the local outlet as well as to remote outlets. However, if the fault interrupter is installed backwards, that is, the designated load connections are attached to the power source and the designated line connections are attached to the remote outlets, then the fault interrupter may not be able to detect and/or interrupt certain classes of faults.
Even in a correctly wired fault interrupter, if the so-called neutral connection is broken or comes loose, then the fault interrupter may not provide fault protection. This is because most fault interrupters require the neutral connection in order to power the detection electronics and in order to source energy to fire the current interruption relay or circuit breaker. If the neutral connection is open (a so-called “open neutral” condition), then a fault may go undetected or, if detected, may not be interrupted.
The present application discloses a fault interrupter which uses a four pole, single throw switch to ensure that the fault interrupter is tolerant to a certain class of misinstallation known as line/load reversal. By adding open neutral detection and a means for detecting if hot and neutral connections are swapped, a high degree of robustness to misinstallation is provided. By adding a redundant circuit breaker mechanism that is engaged in the case of a malfunction in the fault detection electronics, a self-testing capacity may be provided.
Ground fault current interrupts that use a differential transformer to detect the current imbalance that is indicative of a fault condition have been in use since the 1960's. U.S. Pat. No. 3,736,468 (Reeves et al.) discloses a GFCI which uses a differential sense transformer, the secondary of which is amplified to trip a circuit breaker.
A circuit for detecting an open neutral condition and an open ground condition is described in U.S. Pat. No. 4,598,331 (Legatti). That invention relies upon a supplemental secondary winding on the differential transformer to detect an open neutral condition or an open ground condition. When either an open neutral or an open ground condition occurs, an electrical current through the supplemental secondary winding serves to trip a circuit breaker, thereby removing power. One problem with this approach is that if the GFCI is misinstalled with the source and load sides swapped, neither an open ground nor an open neutral condition is detectable. U.S. Pat. No. 6,040,967 (DiSalvo) describes a fault interrupter that prevents the engagement of a circuit breaker reset mechanism in the case of an open neutral condition. This is done by requiring power connections to both hot and neutral in order to latch the circuit breaker into a closed position. If the neutral connection is missing then it is not possible to reset a tripped circuit breaker. However, if the neutral connection is removed while the fault interrupter is in service, there will be no means to detect this condition or to trip the circuit breaker in the case of a fault.
Technologies that detect and indicate the occurrence of a miswiring condition include U.S. Pat. Nos. 3,800,961 (Kershaw) and 5,099,212 (Nagaishi) which disclose systems by which visual indicators can be used to indicate correct (or incorrect) connections to hot, neutral and ground. U.S. Pat. No. 6,560,079 (Hirsh et al.) discloses a system for detecting a loss of ground condition and transposed hot/neutral conductors in an electrical appliance.
The problem of line/load reversal occurs when a fault interrupter that is designed to provide both local power (through one or more faceplate outlets) as well as provide power and protection to downstream outlets, is wired incorrectly. This happens when the power source is connected to the terminals (the load terminals) that are designated to supply downstream electrical power and the down stream load is connected to the terminals (the line terminals) of the fault interrupter that are designated for connection to the power source. Line/load reversal is a problem because it can result in unprotected power to the uSerial
One solution which has been proposed for line/load reversal is the so-called lockout technology described in U.S. Pat. No. 6,245,558 (DiSalvo et al.). This technology requires power to enable a circuit breaker to be engaged after it has been tripped. If a fault interrupter having this technology is installed so that its line terminals are connected to the load side, once the circuit breaker is tripped, there will be no power available to reengage the circuit breaker. Another approach to the problem of line/load reversal is described in U.S. Pat. No. 6,522,510 (Finlay et al.) which uses a resistive element connected at one end to a hot power conductor and on the other end to either a breaker coil or to the gate or base of a switch element. When the fault interrupter is installed with line and load sides reversed, the circuit breaker is tripped, indicating to the installer that an error in installation has been made. The problem with the above two technologies is that while they both have indication means that the fault interrupter has been incorrectly installed, both can provide unprotected power at the local outlet (face power) until such time as the fault interrupter is installed correctly.
Fault interrupters can malfunction, causing the loss of protection against faults. Several solutions to the detection of defective fault interrupters have been proposed. U.S. Pat. Nos. 5,600,524 and 5,715,125 (Neiger, Gershen and Rosenbaum) describe an intelligent GFCI that automatically and periodically tests the fault detection electronics, indicating a malfunction via audible or visual means, and/or by tripping the circuit interruption means or both. The inventions do not test for the correct function of the fault interruption means. U.S. Pat. No. 6,262,871 (Nemir et al.) discloses a fail safe fault interrupter that automatically and periodically tests the fault sensing electronics and that tests for the operation of the fault interruption means and upon the detection of a malfunction, permanently trips a secondary circuit breaker, thereby removing the fault interrupter from service.
3. Objects and Advantages
The present invention encompasses a topology that enables a wall outlet fault interrupter to operate correctly and to provide safety if the line and the load terminals are misconnected, or, equivalently, removes the need to specify line terminals and load terminals. By incorporating open neutral and transversed conductor detection, the fault interrupter will automatically trip so that it never provides unprotected power either to faceplate or to downstream outlets as long as the fault detection/interruption electronics are operational. Finally, by incorporating a secondary system diagnosis and interruption means that is triggered by an auxiliary fault detection mechanism, the entire fault interrupt unit acquires a self-testing capacity. This allows it to fail safe even in the event of a failure of the fault detection electronics. To summarize, the present invention is an electrical fault protection device preferably designed for a wall receptacle implementation that provides the following features:
a) provides a fault detection function and fault interruption function;
b) can provide fault protection to downstream devices;
c) can be installed without regard to line and load sides of the installation;
d) provides ground assurance;
e) will detect an open neutral condition or swapped hot and neutral conductors; and
f) may be provided with a secondary circuit breaker actuation means that can provide redundant protection in the case of circuit malfunction.